The present invention relates to a photovoltaic power generation apparatus, and the design and installation thereof.
The use of photovoltaic power generation apparatuses for housing applications has begun to spread, and research aimed at cost reduction of the apparatuses has been actively performed. As a trump card for the cost reduction, a solar cell module, integrated with a roof material, which obviates the need for a rack, and a non-insulated type inverter, i.e., so-called transless inverter, are being considered for practical use. The efficiency of a transless inverter is high, and transless inverters are inexpensive; therefore, transless inverters have become widely used recently.
FIG. 1 is a block diagram illustrating a configuration of a photovoltaic power generation apparatus which can be tied to a general power system. Electric power is supplied from a solar cell array 1 to a commercial AC power system 3 and/or a load 6 of a customer, supplying electricity, via an inverter 2. Between the inverter 2 and the commercial AC power system 3, earth leakage circuit breakers 4a and 4b are provided, and when a leakage of electricity occurs in a house or building of the customer, the commercial AC power system 3 is completely disconnected.
However, the solar cell array 1 requires a considerably wide outdoor area for installing it, e.g., the solar cell array 1 of 3 kW generation capability requires an area of about 30 m.sup.2, and there is considerably large earth capacitance 5 of the solar cell array 1. Accordingly, there is a fear, as pointed out by Furukawa et al. in the national meeting of the Institute of Electrical Engineers of Japan, Industry Application Society in 1996 (article No. 77), that small leak current flows via the earth capacitance 5 and may unnecessarily activate the earth leakage circuit breaker 4a or 4b (i.e., interrupt the circuit). In a case where the earth leakage circuit breaker 4a is activated in response to leak current via the earth capacitance 5, the load 6 is disconnected from the commercial AC power system 3 and an interruption to service occurs. Further, in a case where the earth leakage circuit breaker 4b is activated, photovoltaic power is disconnected; therefore, the electric power generated by the solar cell array 1 is wasted.
The foregoing problems are specific to a case where a transless inverter which directly connects the solar cell array 1 to the commercial AC power system 3 without an insulating transformer is used. Further, in a solar cell module, integrated with a roof material (referred to as "roof solar cell module" hereinafter), formed in such a manner that solar cells having a metal substrate are encapsulated on a metal reinforcing plate, which is the roof material, with resin, the metal reinforcing plate is grounded; therefore, there is a considerably large capacitance between the metal substrate and the metal reinforcing plate. Accordingly, undesirable operation (circuit interruption) of the earth leakage circuit breaker is apt to be induced as described above.
In the article by Furukawa et al., cause of leak (ground) current and its current value are described, however, there is no mention in the article as to what value of capacitance of the earth capacitance 5 would cause the earth leakage circuit to activate. Therefore, it is unclear as to what capacitance the earth capacitance 5 should be limited to when installing the solar cell array 1.